Interpretive Summary: Depletion of SOC leads to soil quality degradation and declining agronomic/biomass productivity. Therefore, conversion to restorative land uses (e.g., afforestation, improved pastures) and adoption of recommended management practices (RMPs) can enhance SOC and improve soil quality. Important RMPs for enhancing SOC include conservation tillage, mulch farming, cover crops, integrated-nutrient management including use of manure and compost, and agroforestry. Restoration of degraded/desertified soils and ecosystems is an important strategy. In addition, there is a large potential of C sequestration in biomass in forest plantations, short rotation woody perennials etc. The attendant improvement in soil quality with increase in SOC pool size has a strong positive impact on agronomic productivity and world food security. An increase in the SOC pool within the root zone by 1 t C ha-1 yr-1 can enhance food production in developing countries by 30-50 Mt yr-1 including 24-40 Mt yr-1 of cereal and legumes, and 6-10 Mt yr-1 of roots and tubers, while also improving ecosystem services and ensuring sustainable use of soil resources, SOC sequestration also mitigates global warming by off-setting fossil fuel emissions and improving water quality by reducing non-point source pollution.

Technical Abstract:
Most agricultural soils have lost 30 to 75% of their soil organic carbon (SOC) pool, or 30- to 40 t C ha-1. Loss is often greater in soils prone to accelerated erosion and other degradative processes. Globally, CO2 - C emissions since 1850 are estimated at 270 ± 30 Gt from fossil fuel combustion compared with 78 ± 12 Gt from soils and the SOC pool in agricultural soils. Depletion of SOC leads to soil quality degradation and declining agronomic productivity. Conversion to restorative land uses (e.g., afforestation, improved pastures) and adoption of recommended management practices (RMPs) can enhance SOC and improve soil quality. Important RMPs to enhance SOC include conservation tillage, mulch farming, cover crops, integrated-nutrient management including use of manure and compost, and agroforestry. The rate of SOC sequestration ranges from 100 to 1000 kg ha-1 yr-1, depending on climate, soil type, and site-specific management. Total potential of SOC sequestration in the U.S. is 144-432 Mt yr-1 (288 Mt yr-1) comprised of 45-98 Mt in cropland, 13-70 Mt in grazing land and 25-102 Mt in forestland. Global potential of SOC sequestration is estimated at 0.6 to 1.2 Gt C yr-1, comprising 0.4 - 0.8 Gt C yr-1 on cropland (1350 Mha), 0.01 - 0.03 Gt C yr-1 on irrigated soils (275 Mha), and 0.01 - 0.3 Gt C yr-1 through improvements of rangelands and grasslands (3700 Mha). The improvement in soil quality with increase in SOC pool size has a strong positive impact on agronomic productivity and world food security. An increase 1 t SOC ha-1 yr-1 within the root zone can enhance food production in developing countries by 30-50 Mt yr-1 (24-40 Mt yr-1 of cereal and legumes and 6-10 Mt yr-1 of roots and tubers). Despite the enormous challenge, especially in warm and arid regions and predominantly resource-poor farmers, SOC sequestration is a truly win-win strategy. While improving ecosystem services and ensuring sustainable use of soil resources, SOC sequestration also mitigates global warming by off-setting fossil fuel emissions and improving water quality by reducing non-point source pollution. [GRACEnet publication].